Nanotech 2010

Optical properties of silicon nanoparticles: Influence of etching, surface oxidation and surface functionalization

A. Gupta, S. Kluge, C. Schulz, H. Wiggers
Universit├Ąt Duisburg-Essen, DE

Keywords: FTIR, Silicon nanoparticles, Photoluminescence


In this study, we investigated the properties of Si-NPs after surface etching, surface re-oxidation and surface functionalization processes. Surface etching of as-synthesized Si-NPs with hydrofluoric acid causes a blue shift compared to their initial emission spectrum with increased intensity, indicating the etching-induced decrease in nonradiative defects and a slight decrease in the size of Si-NPs. A further size reduction of Si-NPs with a mixture of HF acid and HNO3 acid allowed us to tune the emission from red to green, supporting the origin of orange-to-green photoluminescence (PL) from the quantum confinement effects. Time dependent re-oxidation of orange emitting etched Si-NPs at 620 nm showed the emergence of an additional blue emission at 450 nm. We observed that the main peak at 620 nm shows continuous blue shift in the spectrum with decreased PL intensity, while the peak position at 450 nm was not influenced by the oxidation. These results indicate that orange-to-green emission is associated with quantum size effects while the blue emission is assumed to be related to defect states. In order to stabilize Si-NPs against re-oxidation, the surface must be adequately passivated. Therefore, we terminated the surface of freshly etched Si-NPs with organic molecules by reacting them with alkenes using a thermally induced hydrosilylation process. We find that the surface functionalization using alkenes with ester group provide much better passivation against surface oxidation compared to n-alkenes.
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